Dressings that deliver therapeutic gas to wounds, can be optimized to address conditions that warrant the need to enhance the penetration of the gases into the tissue, to prevent excess moisture from accumulating at the wound site, and to preserve the gas in the reservoir.
Some wounds can be problematic with limited vascular access from underneath to deliver needed nutrients, repair and infection fighting components to the wounds as well as further localized complications that can limit access for topical treatments such as the development of bio-films, dead tissues and variations in tissue depth, shape and local fluid viscosity.
A subset of wounds consist of collaborative communities or organisms (e.g., anaerobic and aerobic bacteria), where various microbes exist where they would not otherwise be able to but for other microbes. For example, aerobic oxygen consuming microbes can proliferate over a surface allowing oxygen sensitive organisms to thrive underneath where more hypoxic conditions can be established (and to a certain extent encased), allowing anaerobes to flourish. In these cases the biofilms act as a barrier so that such that oxygen or any gas in the environment external to the wound cannot reach the target tissue, fluids or cells passively by diffusion.
Some wounds have dead and decaying tissue covering, surrounding or throughout the wounds which also acts as a barrier so that such that oxygen or any metabolic or therapeutic gas in the environment external to the wound cannot get to the target tissue and cells.
Sometimes wound topography varies considerably, where some portions can have a depth that may be minimally impacted by diffusional process from the surface, limiting any metabolic or therapeutic gas in the environment external to the wound from getting to the target tissue and cells.
Other problems exist in that skin or wounds can over time become a source of excess moisture and moisture vapor. When a film or dressing is placed over the wound or skin, excess moisture must be moved away from the wound to prevent maceration of these tissues. Moisture vapor transmission rate (MVTR) through dressings has been an important feature of wound dressings allowing moisture to essentially evaporate as vapor through thin films, foams and microfibers into the surrounding ambient air. The rate of transmission however is dependent upon the external humidity. The drier the ambient air, the greater the diffusion gradient across the film or dressing, and the higher the MVTR. MVTR may be governed by Fick's Law: MVTR=K×ΔP.1 Unfortunately in humid environments the effective MVTR is much lower than that reported in the literature based upon drier laboratory conditions. 1 http://www.pqri.org/pdfs/whitepaper.pdf
For reservoir based gas delivery devices that provide therapeutic gas to a tissue through permeable, porous or perforated surfaces, there is a potential to lose a fraction of the reservoir contents while removing it from the package and securing it onto or into the target tissue. In this case, there is a need for protecting these surfaces from releasing gases contained within or behind prior to delivery to the target tissue.